Fatty acids and alkyl esters thereof are the building blocks for various compositions ranging from lubricants, polymers, solvents, cosmetics and the like. Fatty acids are generally obtained by hydrolysis of triglycerides of vegetable or animal origin. Naturally occurring triglycerides are esters of glycerol and generally straight chain, even numbered carboxylic acids, in size ranging from 10–24 carbon atoms. Most common are fatty acids having 12, 14, 16 or 18 carbon atoms. The fatty acids are either saturated or contain one or more unsaturated bonds.
Long, straight chain saturated fatty acids (C10:0 and higher) are solid at room temperature, which makes them difficult to process in a number of applications. Unsaturated long chain fatty acids, however, e.g. oleic acid are liquid at room temperature, so are easy to process, but are unstable because of the existence of double bond(s). Branched fatty acids mimic the properties of the straight chain unsaturated fatty acids in many respects, but do not have the disadvantage of being unstable. “Branched fatty acids” means fatty acids containing one or more alkyl side groups, and/or aryl groups, which are attached to the carbon chain backbone at any position. Therefore, branched fatty acids are for many applications more desirable than straight chain fatty acids. Commercial branched acids are not, however, naturally occurring materials.
Currently, branched fatty acids are obtained by isomerization (branching) of the straight chain, unsaturated fatty acids having a corresponding chain length. For example, branched C18:0 is prepared from straight C18:1 (or also C18:2). Various routes are known for said isomerization or branching of fatty acids in the art.
In one process, for example, clay is used as a catalyst. Clay catalyzed isomerization suffers, however, from two main disadvantages. First, a considerable amount of undesired side products containing oligomers, saturated straight chain fatty acids and intermediate dimers is formed. A second disadvantage is that the clay catalyst cannot be reused.
U.S. Pat. No. 5,856,539 discloses an isomerization process whereby a fatty acid feed comprising unsaturated fatty acids is contacted with a catalyst, characterized in that the catalyst comprises a material having a microporous structure.
U.S. Pat. No. 5,677,473 describes a process for preparing branched chain fatty acids or alkyl esters thereof which comprises subjecting unsaturated fatty acids having 10–25 carbon atoms or alkyl esters thereof to a skeletal isomerization reaction in the presence of water or a lower alcohol using a zeolite as a catalyst. The zeolite has a linear pore structure of a size small enough to retard dimerization and large enough to allow diffusion of the branched fatty acids or alkyl esters thereof.
U.S. Pat. No. 5,364,949 describes a process for the production of branched fatty acids and their esters, which comprises reacting unsaturated fatty acids or esters thereof with aliphatic nonactivated olefins in the presence of layer silicates and active carbon.
However, all of these processes are plagued by low yield and/or a high rate of undesireable byproduct formation. Accordingly, there is a need for a new process that overcomes these disadvantages, i.e. a process for the preparation of branched fatty acids from straight chain unsaturated fatty acid feedstocks with a high conversion rate, an increased selectivity towards branched monomeric isomers and which employs a reusable catalyst.